5. Energetics 1

Question 1

Define exothermic

Answer 1

A reaction where heat energy is released into the surroundings
Making bonds is an exo process
Enthalpy change is negative

Question 2

Define endothermic

Answer 2

A reaction where heat energy is gained from the surroundings
Breaking bonds is an endo process
Enthalpy change is positive

Question 3

What are standard conditions?

Answer 3

298K
100kPa (1bar)

Question 4

What is enthalpy change of reaction?

Answer 4

The enthalpy change measured at 100kPa and a stated temperature, usually 298K

Question 5

What is enthalpy change of formation?

Answer 5

The enthalpy change when one mole of a substance is formed from its constituent elements in their standard states under standard conditions.

∆rH = ∆fH(products) - ∆fH(reactants)

Question 6

What is enthalpy change of combustion?

Answer 6

The enthalpy change when one mole of a substance is burnt completely in excess oxygen under standard conditions.

∆rH = ∆cH(reactants) - ∆cH(products)

Question 7

What is enthalpy change of solution?

Answer 7

The enthalpy change when one mole of a substance dissolves in water to from an infinitely dilute solution under standard conditions.

∆rH = ∆solH(reactants) - ∆solH(products)

Question 8

What is enthalpy change of neutralisation?

Answer 8

The enthalpy change when one mole of water is formed from the neutralisation of an acid under standard conditions.

Question 9

What is bond enthalpy?

Answer 9

The enthalpy change when one mole of bonds in the gaseous state is broken.

∆rH = ∆bH(bonds broken) - ∆solH(bonds made)

Question 10

What is the first law of thermodynamics?

Answer 10

Energy can be neither created nor destroyed, only transferred.

Question 11

What does Hess’s Law state?

Answer 11

The enthalpy change of a reaction is independent of the path taken provided that the initial and final conditions are the same.